This invention relates to an underfill material for a flip-chip type semiconductor device and a flip-chip type semiconductor device encapsulated therewith.
With the advance of electric equipment toward smaller size, lighter weight and higher performance, the semiconductor mounting technology has changed from the pin mating type to the surface mounting which now becomes the mainstream. One bare chip mounting technology is flip-chip (FC) mounting. The flip-chip mounting is a technique of providing an LSI chip on its circuit pattern-bearing surface with several to several thousands of electrodes, known as bumps, of about 10 to 100 microns high and joining the chip to electrodes on a substrate with a conductive paste or solder. Then the sealing material used for the protection of FC devices must penetrate into gaps of several tens of microns defined by bumps between the substrate and the LSI chip. Conventional liquid epoxy resin compositions used as the underfill material for flip-chip devices are generally composed of a liquid epoxy resin, a curing agent and an inorganic filler. Of these, the most predominant is a composition in which a large amount of inorganic filler is blended in order to provide a matching coefficient of linear expansion with those of semiconductor chips, substrates and bumps for increased reliability.
With respect to stress properties, the flip-chip underfill materials with high loading of filler give rise to no problem. However, they suffer from very low productivity since they have a high viscosity due to the high filler loading so that they may penetrate into the gap between chip and substrate at a very slow rate. There is a desire to overcome this problem.
In the conventional epoxy resin compositions for encapsulating semiconductor devices, it is a common practice to treat the fillers, typically silica with surface modifiers such as silane coupling agents for improving the affinity of the silica surface to epoxy resins and hence, the bond strength therebetween. However, the blending of volatile silane coupling agents in underfill materials gives rise to a problem that even a minor amount of volatiles can cause to create voids since the underfill material is heat cured in a very narrow gap.
An object of the invention is to provide a flip-chip type semiconductor device underfilling material which maintains a low enough viscosity to ensure interstitial infiltration even when filled with a large amount of inorganic filler and which cures into a void-free, reliable product. Another object is to provide a flip-chip type semiconductor device encapsulated with the underfill material and having improved reliability.
It has been found that by blending a liquid epoxy resin with a spherical inorganic filler having a maximum particle size of up to 50 xcexcm and a mean particle size of 0.5 to 10 xcexcm and a reactive functional group-containing silicone compound of the following compositional formula (1) to be defined below instead of a silane coupling agent, there is obtained an underfill material which can infiltrate into narrow gaps even when filled with a large amount of the inorganic filler. This combination minimizes the amount of the alcohol component which would generate when a silane coupling agent is added, and augments the bonds between the surface of inorganic filler and the epoxy resin and between the epoxy resin and the silicon chip. Flip-chip type semiconductor devices encapsulated with the underfill material remain highly reliable because of the absence of voids in the underfill.
Accordingly, the invention provides an underfill material for flip-chip type semiconductor devices, comprising
(A) 100 parts by weight of a liquid epoxy resin,
(B) 100 to 300 parts by weight of a spherical inorganic filler having a maximum particle size of up to 50 xcexcm and a mean particle size of 0.5 to 10 xcexcm,
(C) 0.1 to 6 parts by weight of a reactive functional group-containing silicone compound of the following compositional formula (1):
R1aR2bSi(OR3)c(OH)dO(4xe2x88x92axe2x88x92bxe2x88x92cxe2x88x92d)/2xe2x80x83xe2x80x83(1)
wherein R1 is a monovalent organic group having a reactive functional group, R2 and R3 are independently unsubstituted or alkoxy-substituted monovalent hydrocarbon groups of 1 to 8 carbon atoms, a is a number of 0.16 to 1.0, b is a number of 0 to 2.0, c is a number of 0.5 to 2.0, a is a number of 0 to 1.0, and a+b+c+d is 0.8 to 3, the number of silicon atoms per molecule being from 2 to 6, and
(D) 0.01 to 10 parts by weight of a curing accelerator.
Also contemplated herein is a flip-chip type semiconductor device sealed with the underfill material in a cured state.